Centralizer having atmospheric chamber for expansion in response to hydrostatic pressure

ABSTRACT

A centralizer for use in a wellbore includes: a body for disposing around a periphery of a casing or liner string, the body having a plurality of bow springs biased toward an expanded position; a mandrel for disposing around the periphery of the casing or liner string; a piston disposed around the mandrel and movable between a locked position and a release position; a plurality of dogs, each dog mounted to or formed integrally with the respective bow spring and captured by the piston in the locked position, thereby keeping the bow springs in a retracted position; an atmospheric chamber formed between the piston and the mandrel; and a fastener for releasably connecting the piston to the mandrel in the locked position.

BACKGROUND OF THE DISCLOSURE Field of the Disclosure

The present disclosure generally relates to a centralizer having atmospheric chamber for expansion in response to hydrostatic pressure.

Description of the Related Art

U.S. Pat. No. 4,523,640 discloses a well logging instrument including a body member supporting one or more arm members which may be biased outwardly against the sidewalls of the borehole. The arm members may be held in a closed position, adjacent the body member, during entry into a borehole by a heat sensitive retaining member. As the instrument is exposed to borehole temperature the heat sensitive retaining member will within a preselected temperature range release the arm member allowing the arm members to expand outwardly from the body member into contact with the sides of the borehole.

U.S. Pat. No. 5,097,905 discloses a centralizer for well casing including an externally threaded upper anchor fixed to the casing, an upper collar threaded to the upper anchor, a lower anchor fixed to the casing, a lower collar bearing against said lower anchor, and a plurality of relatively flexible metallic straps extending between the collars. The centralizer is assembled over a section of well casing as the casing is lowered into the well. When the casing reaches its final depth, it is rotated so that the anchors rotate with the casing, while the collars and the straps remain stationary, as the straps engage the wellbore. When the casing is thus rotated, the upper collar moves along the threads of the upper anchor towards the lower collar, axial movement of which is prevented by the lower anchor. This forces the straps to bulge outwardly away from the casing, urging the casing toward the center of the borehole.

U.S. Pat. No. 5,261,488 discloses, at FIGS. 18 and 18A and col. 7, line 40-col. 8, line 2, a centralizer restrained in a retracted position by a strap which is released by a piston operated by hydrostatic pressure.

U.S. Pat. No. 8,360,161 discloses a temperature activated actuator installed on a tubular to actuate an adjacent device may include one or more shape-memory alloy elements. The elements may be coupled between a first portion and a second portion of a device, or the elements may be coupled between the tubular and a portion of the device. The elements are activated by raising the temperature to a transition temperature to cause metallurgical phase transformation, causing the elements to shrink and displace at least a portion of the device. The actuator may be used, for example, to actuate a centralizer from a run-in mode to a deployed mode or, alternately, to actuate a packing member from a run-in mode to an isolating mode. A nickel-titanium alloy, for example, may be used as the shape-memory alloy material from which the shape-memory element is made.

U.S. Pat. No. 9,580,976 discloses a centralizer assembly that allows for the assembly to be deployed in-situ. The centralizer assembly includes flexible members that can be extended into the well bore in situ by the initiation of a gas generating device. The centralizer assembly can support a large load carrying capability compared to a traditional bow spring with little or no installation drag. Additionally, larger displacements can be produced to centralize an extremely deviated casing.

US 2015/0034336 discloses a centralizer having bow springs in a retracted position to facilitate passage through a restriction. After passing through the restriction, the bow springs may be expanded to support a casing. In one embodiment, the bow springs may be expanded using a movable sleeve.

SUMMARY OF THE DISCLOSURE

The present disclosure generally relates to a centralizer having atmospheric chamber for expansion in response to hydrostatic pressure. In one embodiment, a centralizer for use in a wellbore includes: a body for disposing around a periphery of a casing or liner string, the body having a plurality of bow springs biased toward an expanded position; a mandrel for disposing around the periphery of the casing or liner string; a piston disposed around the mandrel and movable between a locked position and a release position; a plurality of dogs, each dog mounted to or formed integrally with the respective bow spring and captured by the piston in the locked position, thereby keeping the bow springs in a retracted position; an atmospheric chamber formed between the piston and the mandrel; and a fastener for releasably connecting the piston to the mandrel in the locked position.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments.

FIG. 1 illustrates a casing or liner string equipped with a plurality of centralizers, each centralizer having an atmospheric chamber for expansion in response to hydrostatic pressure, according to one embodiment of the present disclosure.

FIGS. 2A, 2B, and 3A illustrate a typical one of the centralizers in the retracted position.

FIGS. 2C, 2D, and 3B illustrate the typical one of the centralizers in the expanded position.

DETAILED DESCRIPTION

FIG. 1 illustrates a casing or liner string 1 equipped with a plurality of centralizers 2 a-e, each centralizer having an atmospheric chamber 8 (FIG. 3A) for expansion in response to hydrostatic pressure, according to one embodiment of the present disclosure. The centralizers 2 a-e may each be mounted to the casing or liner string 1 along at least a portion thereof that will be cemented into a wellbore (not shown). The centralizers may be spaced along the portion of the casing or liner string 1 at regular intervals. Each centralizer 2 a-e may be initially restrained in a retracted position (centralizers 2 a-c) and may actuate to an expanded position (centralizers 2 d,e) in response to being lowered past an actuation depth 3 in the wellbore. Each centralizer 2 a-e may be set to actuate to the expanded position at the same actuation depth 3 or the centralizers may be set to different depths depending on their position along the casing or liner string 1. Having the centralizers 2 a-e in the retracted position reduces frictional resistance when lowering the casing or liner string 1 into the wellbore and/or may safeguard against damage from the expanded centralizers scraping against sensitive components, such as seal bores in the wellhead.

FIGS. 2A, 2B, and 3A illustrate a typical one 2 of the centralizers 2 a-e in the retracted position. The typical centralizer 2 may include a pair of collars 4 p,w, a body 5, a plurality of dogs 6, a piston 7 p, a mandrel 7 m, an atmospheric chamber 8, a shearable fastener 9, and an anchor 10. The body 5 may have a pair of end rings 5 p,w and a plurality of bow springs 5 b extending therebetween. The bow springs 5 may be spaced around the body 5 at regular intervals (eight bow springs spaced at forty-five degree intervals shown). Bypass passages may be formed between the bow springs 5 b to accommodate fluid flow through an annulus formed between the casing or liner string 1 and the wellbore. The bow springs 5 b may each be identical and radially movable between an expanded position (FIGS. 2C, 2D, and 3B) and the retracted position (shown). The bow springs 5 b may have a parabolic shape in the expanded position.

The body 5 may longitudinally extend when moving from the expanded position to the retracted position and longitudinally contract when moving from the retracted position to the expanded position. The bow springs 5 b may be naturally biased toward the expanded position and an expanded diameter of the centralizer 2 may correspond to a diameter of the wellbore. Engagement of the bow springs 5 b with a wall of the wellbore may move the casing or liner string 1 toward a central position within the wellbore to ensure that a uniform cement sheath is formed around the casing or liner string 1 during the cementing operation. The body 5 may be formed from a single sheet of spring steel by cutting out slots to form strips which will become the bow springs 5 b. The body 5 may be formed into a tubular shape by rolling the cut sheet and welding seams of the end rings 5 p,w together. The bow springs 5 b may have the natural bias toward the expanded position by being held therein during heat treatment of the body 5.

After the body 5 has been formed, each collar 4 p,w may be inserted into the respective end rings 5 p,w. Each collar 4 p,w may be formed to be a tight fit within the end rings 5 p,w. Each collar 4 p,w may then be spot-welded to the respective end rings 5 p,w. A lip of each end ring 5 p,w extending past the respective collar 4 p,w may be split into a multitude of tabs (before or after insertion of the collars) and the tabs may be bent over the respective collar, thereby mounting the collars to the body 5 (in addition to the spot welds). The anchor 10 may include a locking ring 10 r and a plurality of set screws 10 s. The locking ring 10 r may have a plurality of threaded sockets formed through a wall thereof and spaced therearound. The set screws 10 s may be driven into the threaded sockets and into engagement with a periphery of the casing or liner string 1, thereby mounting the locking ring 10 r to the casing or liner string. The locking ring 10 r may be located between the collars 4 p,w by insertion through one of the slots between the bow springs 5 b before the centralizer 2 is slid over the periphery of the casing of liner string 1. Setting of the anchor 10 may trap the centralizer 2 into place along the casing or liner string 1 while allowing limited longitudinal movement of the body 5 relative thereto to accommodate movement between the positions.

One of the dogs 6 may be mounted to each bow spring 5 b at a mid portion thereof. The mid portion of each bow spring 5 b may have a groove formed therein for receiving the respective dog 6 and each dog may be mounted to the respective bow spring, such as by welding. The mandrel 7 m may be disposed around the periphery of the casing or liner sting 1 and may be located between the anchor 10 and the upper collar 4 p. The mandrel 7 m may abut the locking ring 10 r when the centralizer 2 is in the retracted position. The mandrel 7 m may have a reduced outer diameter upper sleeve, an enlarged outer diameter lower foot, and a shoulder connecting the sleeve and the foot. The foot of the mandrel 7 m may have an upper groove formed in a periphery thereof and a lower groove formed in the periphery thereof. The upper groove of the mandrel 7 m may carry an elastomeric seal 11, such as an o-ring, and the lower groove may carry the shearable fastener 9, such as a shear ring.

Alternatively, each dog 6 may be formed integrally with the respective bow spring 5 b. Alternatively, each dog 6 may be mounted to the respective bow spring 5 b by having wings wrapped around the respective bow spring instead of by welding.

The piston 7 p may be disposed around the periphery of the mandrel 7 m and may be located between the anchor 10 and the upper collar 4 p. The piston 7 p may have a reduced inner diameter upper head, an enlarged inner diameter lower sleeve, and a shoulder connecting the sleeve and the head. The head of the piston 7 p may have a groove formed in an inner surface thereof. The groove of the piston 7 p may carry an elastomeric seal 11, such as an o-ring. The head diameter of the piston 7 p may correspond to the sleeve diameter of the mandrel 7 m and the sleeve diameter of the piston may correspond to the foot diameter of the mandrel. The piston 7 p may be longitudinally moveable relative to the mandrel 7 m between an upper locked position (shown) and a lower release position (FIGS. 2D and 3B). The head of the piston 7 p may trap the dogs 6 therein in the locked position, thereby restraining the bow springs 5 b in the retracted position against their natural bias toward the expanded position. To reduce friction and/or so the dogs 6 exert a downward force on the piston 7 p, an inner surface of the head of the piston may have a conical portion for receiving the dogs and an outer surface of each dog may have an inclined portion for engagement with the conical portion of the head.

Alternatively, the inner surface of the head of the piston 7 p may have a straight portion for receiving the dogs 6 and the outer surface of each dog may have a straight portion for engagement with the straight portion of the head or the inner surface of the head of the piston may be partially straight and partially conical and the outer surface of each dog may be partially straight and partially inclined.

The atmospheric chamber 8 may be formed radially between the sleeves of the mandrel 7 m and the piston 7 p and longitudinally between the shoulders of the mandrel and the piston. Interfaces between the piston 7 p and the mandrel 7 m may be sealed by engagement of the seal 11 of the mandrel 7 m with the sleeve of the piston 7 p and by engagement of the seal of the piston with the sleeve of the mandrel. The head of the piston 7 p may be exposed to hydrostatic pressure during lowering of the centralizer 2 into the wellbore. To set the piston 7 p, the piston may be in the release position while the bow springs 5 b are retracted using a strap. The piston 7 m may then be moved to the locked position and the shearable fastener 9 then inserted into the lower groove of the mandrel 7 m. To facilitate assembly, the shearable fastener 9 may be a snap ring. The strap may then be released from the bow springs 5 b. An outer diameter of the shearable fastener 9 may correspond to an outer diameter of the piston 7 p such that the shearable fastener releasably connects the piston to the mandrel 7 m, thereby preventing movement of the piston from the locked position to the release position.

FIGS. 2C, 2D, and 3B illustrate the typical one 2 of the centralizers 2 a-e in the expanded position. As the centralizer 2 reaches the actuation depth 3, the force exerted on the piston 7 p by the hydrostatic pressure acting on the head thereof reaches a threshold force to fracture the shearable fastener 9, thereby allowing the piston 7 p to move downward from the locked position to the release position and releasing the dogs 6 from captivity. The natural bias of the bow springs 5 b may move the centralizer 2 from the retracted position toward the expanded position (or at least until stopped by engagement of the bow springs with the wall of the wellbore).

Additionally, since the mandrel 7 m may not be anchored to the locking ring 10 r, hydrostatic pressure may exert a force on the foot thereof which may push the mandrel toward the piston 7 p, thereby effectively increasing an area of the piston.

Alternatively, the casing or liner string 1 may be lowered to a deployment depth with all of the centralizers 2 a-e still in the retracted position and then annulus or hydrostatic pressure in the wellbore may be increased to actuate the piston 7 p. The annulus pressure may be increased by closing a blowout preventer and circulating fluid down the casing or liner string 1 and through a choke line of the wellhead. The hydrostatic pressure may also be increased by lowering the casing or liner string with a less dense fluid in the wellbore and then replacing the less dense fluid with a more dense fluid after the casing or liner string has been lowered to the deployment depth.

While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope of the invention is determined by the claims that follow. 

1. A centralizer for use in a wellbore, comprising: a body for disposing around a periphery of a casing or liner string, the body having a plurality of bow springs biased toward an expanded position; a mandrel for disposing around the periphery of the casing or liner string; a piston disposed around the mandrel and movable between a locked position and a release position; a plurality of dogs, each dog mounted to or formed integrally with the respective bow spring and captured by the piston in the locked position, thereby keeping the bow springs in a retracted position; an atmospheric chamber formed between the piston and the mandrel; and a fastener for releasably connecting the piston to the mandrel in the locked position.
 2. The centralizer of claim 1, wherein: an inner surface of the piston has a portion for receiving the dogs, and an outer surface of each dog has a portion for engagement with the portion of the inner surface of the piston.
 3. The centralizer of claim 2, wherein: the portion of the inner surface of the piston is at least partially conical, and the portion of the outer surface of each dog is at least partially inclined.
 4. The centralizer of claim 1, wherein: the body further has a pair of end rings, and the centralizer further comprises a pair of collars, each collar mounted to the respective end ring.
 5. The centralizer of claim 4, further comprising the casing or liner string; and further comprising an anchor engaged with the periphery of the casing or liner string, wherein the anchor is disposed between the collars.
 6. The centralizer of claim 5, wherein the mandrel abuts the anchor when the bow springs are in the retracted position.
 7. A method of installing a casing or liner string into a wellbore, comprising: forming an assembly comprising the casing or liner string and the centralizer of claim 1 in the retracted position; and lowering the assembly into the wellbore, wherein upon reaching an actuation depth, hydrostatic pressure exerted on the piston releases the fastener and moves the piston from the locked position to the release position, thereby freeing the dogs and allowing the bow springs to move toward the expanded position.
 8. A method of installing a casing or liner string into a wellbore, comprising: forming an assembly comprising the casing or liner string and the centralizer of claim 1 in the retracted position; lowering the assembly into the wellbore, wherein the centralizer remains in the retracted position; and after lowering the assembly to a deployment depth, increasing pressure in the wellbore, wherein the increased pressure in the wellbore is exerted on the piston, thereby releasing the fastener, moving the piston from the locked position to the release position, freeing the dogs, and allowing the bow springs to move toward the expanded position. 